top of page

Public Comments on California’s New Vapor Draft Intrusion Guidance: What Next?

Updated: Feb 2, 2022

By Catherine W. Johnson

Public comments on California’s Draft Supplemental Vapor Intrusion Guidance (“DSVIG”) were due to Cal-EPA by June 1, 2020.[1] So far, comments submitted indicate several California businesses and industries are concerned about the costs to implement the new proposed guidance, asserting the guidance will require substantial investigation of sites that pose little or no risk. Many commenters dispute the validity and relevance of the U.S. EPA attenuation factor of 0.03 proposed for use (i.e., an estimate of the decimal fraction of vapor phase chemicals that will pass through a barrier and enter the indoor space of a structure) – and assert the guidance is an “underground regulation” (i.e., a de facto rule which is adopted without adhering to the rulemaking process required by the California Administrative Procedure Act).

California regulatory agencies (including the State Water Resources Board, the Department of Toxic Substances Control and the San Francisco Bay Regional Water Quality Control Board (RWQCB)) have been developing the new guidance since at least 2014. Although the draft guidance was not released until February 2020, some agencies (including the San Francisco Bay RWQCB) have already been requiring the regulated community to comply with elements of the guidance – most notably collecting indoor air samples rather than relying on sub-slab samples.

Several commenters – including the California Chamber of Commerce, some consulting firms, and associations representing certain real estate/development interests and industries (e.g., chemical, refining) – requested the opportunity for input from private sector stakeholders. Some identified limitations or deficiencies in the U.S. EPA attenuation factor, including the lack of data points about California-specific conditions and advances in sampling collection methodologies since the U.S. EPA data was collected. Many commenters also asked for further extensions before the guidance is finalized – noting that the California-specific database under development by DTSC should be evaluated before Cal-EPA adopts a default attenuation factor.

Some commenters criticized the guidance's preference for mitigation supplemented by remediation rather than reliance on mitigation and land use covenants. At least one commenter queried whether application of the EPA attenuation factor coupled with a preference for remediation could result in the anomalous situation where a robust vapor intrusion mitigation system (VIMS) was in place yet a remediation system might need to continue to operate indefinitely despite non-detectable concentrations of chemicals inside the building.

Finally, some commentators asserted that the guidance was too prescriptive for a guidance document and that more alternatives should be identified in the guidance – or that the matter should be referred to individual regulatory agencies and go through the rulemaking process. Others more directly asserted the guidance was an underground regulation. In either case, some commentators may either be evaluating the possibility of a legal challenge to the guidance as an underground rule – or hoping the threat of such a challenge will motivate Cal-EPA to incorporate more alternatives than are presented in the current guidance and/or adopt some of the other changes commenters contend are necessary.

In conclusion, it remains to be seen what will happen next. Stay tuned.

[1] Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion (February 2020)


The opinions expressed are those of the author and do not necessarily reflect the views of the firm, its clients, or any of its or their respective affiliates. This article is for general information purposes and is not intended to be and should not be taken as legal advice.

bottom of page